Project Summary It is well recognized that current batteries of genetic toxicology assays exhibit two critical deficiencies. First, the throughput capacity of in vitro mammalian cell genotoxicity tests is low, and does not meet current needs. Second, conventional assays provide simplistic binary calls, genotoxic or non-genotoxic. In this scheme there is little or no consideration for potency, and virtually no information is provided about molecular targets and mechanisms. These deficiencies in hazard characterization prevent genotoxicity data from optimally contributing to modern risk assessments, where this information is essential. We will address these major problems with current in vitro mammalian cell genetic toxicity assays by developing methods and associated commercial assay kits that dramatically enhance throughput capacity, and delineate genotoxicants' primary molecular targets, while simultaneously providing information about potency. Once biomarkers and a family of multiplexed assays have been developed for these purposes, an interlaboratory trial will be performed with prototype assay kits to assess the transferability of the methods.